1. Field of the Invention
The present invention is directed to hydraulic lash adjusters used in the valve trains of internal combustion engines and more particularly to a self-contained hydraulic lash adjuster of the type having a pressure chamber, a reservoir chamber and floating means within said reservoir chamber to prevent the absorption of air into the fluid during operation of the engine.
2. Prior Art
In the valve trains of internal combustion engines predetermined valve clearances are generally provided in order to compensate for thermal expansion of various parts in the valve trains. However, since excess lash may be generated due to the valve clearances in the valve trains during engine operation hydraulic lash adjusters have been used for automatically taking up the valve clearances in the valve trains thereby preventing any possible lash in stabilizing the opening and closing operation of the engine intake and exhaust valves. The elimination of excess lash prevents undesirable power losses and undesirable noises which might otherwise occur during the operation of the engine.
Conventional self-contained lash adjuster devices generally include a pressure chamber and a reservoir chamber containing an hydraulic fluid with the two chambers being disposed in communication with each other through an opening controlled by means of a one-way check valve which will allow the flow of fluid from the reservoir chamber to the pressure chamber. The flow of fluid from the pressure chamber to the reservoir chamber generally takes place through a leakage clearance between a plunger containing the reservoir chamber and the housing and a passage through the wall of the plunger. However, such conventional lash adjuster devices suffer from the disadvantage that air can be absorbed into the hydraulic fluid which is generally a silicon oil having a high viscosity which will then impair the effective operation of the lash adjuster. When the capacity of the pressure chamber suddenly increases due to upward movement of the plunger any air within the reservoir chamber will become absorbed into or entrained by the high viscosity oil as it flows into the pressure chamber. Such an absorption of air creates undesirable tapping sounds in the operation of the lash adjuster and leads to inferior operating qualities.
An example of a self-contained hydraulic lash adjuster is disclosed in the U.S. Pat. No. 4,191,142 to Kodama. The lash adjuster disclosed in the Kodama patent includes a cylinder member and a plunger member slidably fitted therein to define a fluid pressure chamber between the end walls thereof. The plunger member is provided with a reservoir chamber and an elastic bag member is disposed within the reservoir chamber with the inner surface of the elastic bag member being normally in communication with atmospheric pressure while the outer surface thereof is disposed in contact with the fluid reservoir chamber. While the elastic bag member will compensate for changes in the fluid volume in the reservoir chamber during operation there is still the possibility of air within the reservoir chamber becoming absorbed into or entrained by the hydraulic fluid during operation.